Structural units and properties of BaF2–PbF2–B2O3 glasses

Abstract Glasses of the composition xBaF2⋅(45 − x)PbF2⋅55B2O3 (0 ≤ x ≤ 45 mol%) have been investigated. XRD revealed amorphous structure for x ≤ 40 mol% and formation of crystalline BaF2 phase at 45 mol% BaF2. SEM and EDP micrographs indicated low degree of crystallinity in 45PbF2⋅55B2O3 glass and intense crystallinity in 45BaF2⋅55B2O3 glass. Both these phases are dispersed in the amorphous borate matrix. It is deduced from FTIR spectra that PbF2 and BaF2 partially modify the borate network forming Pb1/22 +[BO3F]− and Ba1/22 +[BO3F]− units, respectively. The rest of PbF2 and BaF2 build individual amorphous matrices, in which the related crystalline phases can be formed. The fraction N4 of four coordinated boron atoms (determined from FTIR spectra and 11B MAS NMR) does not change with replacing BaF2 for PbF2. N4 values have been used to calculate the fractions of all units in the glass structure. Density and molar volume obtained by using these fractions and unit volume agree well with the experimental data. The electrical conductivity decreases while the activation energy for conduction increases at different rates upon increasing BaF2 content. These changes are correlated with the transport of F− ions in PbF2 and BaF2 former matrices. The conductivity in the studied glasses is mainly controlled by the activation energy.